encapsulated carcinoma of follicular cell origin

Definition: Encapsulated carcinomas of follicular cell origin include an encapsulated/well-circumscribed (E/WC) follicular variant of papillary carcinoma (FV-PTC) and encapsulated follicular and Hurthle cell carcinoma (EFTC, EHTC respectively).

FVPTC usually presents as an E/WC tumor and less commonly as an infiltrative neoplasm. E/WC FVPTC rarely metastasizes to lymph nodes, whereas infiltrative tumors often present with cervical nodal metastases.

Many studies revealed FVPTC in general to be genetically close to the follicular adenomas (FA)/EFC group of tumors.

This is particularly true for the E/WC FVPTC which has a high rate of RAS and lack BRAFV600E mutations.

Infiltrative FVPTC has an opposite molecular profile closer to classical papillary carcinoma than to FA/EFC (BRAFV600E > RAS mutations).

Non-invasive E/WC FVPTCs are extremely indolent even if treated with lobectomy alone.

While EFC and EHC with capsular invasion only have an excellent outcome, those with extensive (≥4 foci) lymphovascular invasion (LVI) have a significant rate of distant recurrence.

The prognosis of those with focal LVI seems good, but more studies are needed to confirm their behavior.

In EHC, those with extensive/significant LVI have a different RNA expression profile than those with less LVI.

EHC appear to recur earlier, are less RAI avid, and have a different mutation profile than EFC.

Noninvasive E/WC FVPTC should be treated conservatively.

There is therefore a need to reclassify the E/WC FVPTC in order to prevent overtreatment. In view of their molecular and behavioral differences, EHC should not be considered a subset of EFC.

References

 Encapsulated Thyroid Carcinoma of Follicular Cell Origin. Xu B, Ghossein R. Endocr Pathol. 2015 Sep;26(3):191-9. doi : 10.1007/s12022-015-9376-5 PMID: 26003547